Neutrino-driven supernova of a low-mass iron-core progenitor boosted by three-dimensional turbulent convection

We present the first successful simulation of a neutrino-driven supernova explosion in three dimensions (3D), using the Prometheus-Vertex code with an axis-free Yin-Yang grid and a sophisticated treatment of three-flavor, energy-dependent neutrino transport. The progenitor is a nonrotating, zero-metallicity 9.6 Msun star with an iron core. While in spherical symmetry outward shock acceleration sets in later than 300 ms after bounce, a successful explosion starts at ~130 ms postbounce in two dimensions (2D). The 3D model explodes at about the same time but with faster shock expansion than in 2D and a more quickly increasing and roughly 10 percent higher explosion energy of >10^50 erg. The more favorable explosion conditions in 3D are explained by lower temperatures and thus reduced neutrino emission in the cooling layer below the gain radius. This moves the gain radius inward and leads to a bigger mass in the gain layer, whose larger recombination energy boosts the explosion energy in 3D. These differences are caused by less coherent, less massive, and less rapid convective downdrafts associated with postshock convection in 3D. The less violent impact of these accretion downflows in the cooling layer produces less shock heating and therefore diminishes energy losses by neutrino emission. We thus have, for the first time, identified a reduced mass accretion rate, lower infall velocities, and a smaller surface filling factor of convective downdrafts as consequences of 3D postshock turbulence that facilitate neutrino-driven explosions and strengthen them compared to the 2D case.Comment: 7 pages, 5 figures; revised version with more discussion of resolution dependence and differences to other 3D results; accepted by ApJ

Resolution Study for Three-dimensional Supernova Simulations with the Prometheus-Vertex Code

We present a carefully designed, systematic study of the angular resolution dependence of simulations with the Prometheus-Vertex neutrino-hydrodynamics code. Employing a simplified neutrino heating-cooling scheme in the Prometheus hydrodynamics module allows us to sample the angular resolution between 4 degrees and 0.5 degrees. With a newly-implemented static mesh refinement (SMR) technique on the Yin-Yang grid, the angular coordinates can be refined in concentric shells, compensating for the diverging structure of the spherical grid. In contrast to previous studies with Prometheus and other codes, we find that higher angular resolution and therefore lower numerical viscosity provides more favorable explosion conditions and faster shock expansion. We discuss the possible reasons for the discrepant results. The overall dynamics seem to converge at a resolution of about 1 degree. Applying the SMR setup to marginally exploding progenitors is disadvantageous for the shock expansion, however, because kinetic energy of downflows is dissipated to internal energy at resolution interfaces, leading to a loss of turbulent pressure support and a steeper temperature gradient. We also present a way to estimate the numerical viscosity on grounds of the measured turbulent kinetic-energy spectrum, leading to smaller values that are better compatible with the flow behavior witnessed in our simulations than results following calculations in previous literature. Interestingly, the numerical Reynolds numbers in the turbulent, neutrino-heated postshock layer (some 10 to several 100) are in the ballpark of expected neutrino-drag effects on the relevant length scales in the turbulent postshock layer. We provide a formal derivation and quantitative assessment of the neutrino drag terms in an appendix.Comment: 37 pages, 14 figures, 4 tables; revised version with neutrino drag discussion extended for numerical evaluation; accepted by Ap

Parallelized Solution Method of the Three-dimensional Gravitational Potential on the Yin-Yang Grid

We present a new method for solving the three-dimensional gravitational potential of a density field on the Yin-Yang grid. Our algorithm is based on a multipole decomposition and completely symmetric with respect to the two Yin-Yang grid patches. It is particularly efficient on distributed-memory machines with a large number of compute tasks, because the amount of data being explicitly communicated is minimized. All operations are performed on the original grid without the need for interpolating data onto an auxiliary spherical mesh.Comment: 8 pages, 4 figures; two minor additions after refereeing; accepted by Ap

Effects of LESA in Three-Dimensional Supernova Simulations with Multi-Dimensional and Ray-by-Ray-plus Neutrino Transport

A set of eight self-consistent, time-dependent supernova (SN) simulations in three spatial dimensions (3D) for 9 solar-mass and 20 solar-mass progenitors is evaluated for the presence of dipolar asymmetries of the electron lepton-number emission as discovered by Tamborra et al. and termed lepton-number emission self-sustained asymmetry (LESA). The simulations were performed with the Aenus-Alcar neutrino/hydrodynamics code, which treats the energy- and velocity-dependent transport of neutrinos of all flavors by a two-moment scheme with algebraic M1 closure. For each of the progenitors, results with fully multi-dimensional (FMD) neutrino transport and with ray-by-ray-plus (RbR+) approximation are considered for two different grid resolutions. While the 9 solar-mass models develop explosions, the 20 solar-mass progenitor does not explode with the employed version of simplified neutrino opacities. In all 3D models we observe the growth of substantial dipole amplitudes of the lepton-number (electron neutrino minus antineutrino) flux with stable or slowly time-evolving direction and overall properties fully consistent with the LESA phenomenon. Models with RbR+ transport develop LESA dipoles somewhat faster and with temporarily higher amplitudes, but the FMD calculations exhibit cleaner hemispheric asymmetries with a far more dominant dipole. In contrast, the RbR+ results display much wider multipole spectra of the neutrino-emission anisotropies with significant power also in the quadrupole and higher-order modes. Our results disprove speculations that LESA is a numerical artifact of RbR+ transport. We also discuss LESA as consequence of a dipolar convection flow inside of the nascent neutron star and establish, tentatively, a connection to Chandrasekhar's linear theory of thermal instability in spherical shells.Comment: 20 pages, 9 figures; revised version accepted by ApJ; new Figs. 6,7, and new panels in Fig.8 added; Sects. 4,5,6 considerably extended in reply to referee question

Large-Scale Mixing in a Violent Oxygen-Neon Shell Merger Prior to a Core-Collapse Supernova

We present a seven-minute long $4\pi$-3D simulation of a shell merger event in a non-rotating $18.88\, M_\odot$ supernova progenitor before the onset of gravitational collapse. The key motivation is to capture the large-scale mixing and asymmetries in the wake of the shell merger before collapse using a self-consistent approach. The $4\pi$ geometry is crucial as it allows us to follow the growth and evolution of convective modes on the largest possible scales. We find significant differences between the kinematic, thermodynamic and chemical evolution of the 3D and the 1D model. The 3D model shows vigorous convection leading to more efficient mixing of nuclear species. In the 3D case the entire oxygen shell attains convective Mach numbers of $\mathord{\approx}\, 0.1$, whereas in the 1D model, the convective velocities are much lower and there is negligible overshooting across convective boundaries. In the 3D case, the convective eddies entrain nuclear species from the neon (and carbon) layers into the deeper part of the oxygen burning shell, where they burn and power a violent convection phase with outflows. This is a prototypical model of a convective-reactive system. Due to the strong convection and the resulting efficient mixing, the interface between the neon layer and the silicon-enriched oxygen layer disappears during the evolution, and silicon is mixed far out into merged oxygen/neon shell. Neon entrained inwards by convective downdrafts burns, resulting in lower neon mass in the 3D model compared to the 1D model at time of collapse. In addition, the 3D model develops remarkable large-scale, large-amplitude asymmetries, which may have important implications for the impending gravitational collapse and the subsequent explosion.Comment: 23 pages, 18 figure, Accepted to The ApJ (matches the accepted version

Modellierung neutrinogetriebener Kernkollaps-Supernova-Explosionen in drei Dimensionen

Core-collapse supernovae are tremendous explosions of massive stars. Their explosion mechanism is matter of intense research and can only be studied in detail with the help of computer simulations. In this thesis, we present the first successfully exploding three-dimensional core-collapse supernova simulations performed with sophisticated neutrino transport. Comparisons to axially symmetric models and non-exploding cases reveal how hydrodynamic instabilities and neutrino interactions affect the explosion process.Kernkollaps-Supernovae sind gewaltige Explosionen massereicher Sterne. Ihr Explosionsmechanismus ist Gegenstand intensiver Forschung und kann nur mittels Computersimulationen im Detail untersucht werden. In dieser Arbeit werden die ersten erfolgreich explodierenden dreidimensionalen Simulationen von Kernkollaps-Supernovae beschrieben, die mit hochentwickeltem Neutrinotransport durchgeführt wurden. Vergleiche zu axialsymmetrischen Modellen und fehlgeschlagenen Explosionen zeigen auf, wie hydrodynamische Instabilitäten und Neutrino-Wechselwirkungen den Explosionsprozess beeinflussen

The 82nd International Labour Conference Amnesty International's concerns relevant to the Committee on Application of Standards

SIGLEAvailable from British Library Document Supply Centre- DSC:0859.3885(AI-IOR--42/01/95) / BLDSC - British Library Document Supply CentreGBUnited Kingdo